The study of stem cell and neuro-vascular development

National Heart, Lung, And Blood Institute

Investigators

Linked publications, trials & patents

Abstract

1) CXCL12-CXCR4 signaling controls organ-specific blood vessel patterning. We and others have previously discovered the essential role of chemokine CXCL12-CXCR4 signaling in organ-specific patterns of arterial branching: in the developing skin vasculature, sensory nerve-derived CXCL12 recruits its receptor CXCR4+ endothelial cells to form arteries to align with the nerves (Li et al. Dev Cell 2013). Moreover, endothelial cell-specific gain- and loss-of-function Cxcr4 mutations lead to impaired blood vessel patterning in the developing skin and coronary vasculature, suggesting that appropriate CXCR4 expression in the appropriate endothelial cell type is required for organ-specific vessel patterning (Li et al. Dev Biol 2021). We are currently investigating what controls endothelial CXCR4 expression in vascular development. Given that CXCR4 is a well-known hypoxia-responsive gene and an enhanced CXCR4 expression is detectable in endothelial cell culture with a low-oxygen chamber (1%), we are currently focusing on how oxygen sensing pathway influences CXCR4 expression in endothelial cells. Interestingly, endothelial cell-specific loss-of-function mutation of von Hippel-Landau tumor suppressor protein (pVHL), a key player in the cellular response to oxygen sensing, leads to constitutive HIF transcription factor stabilization and aberrant upregulation of CXCR4 in endothelial cells. Indeed, endothelial cell-specific gain-of-function Cxcr4 mutation exhibits an almost identical phenotype (Li et al. Manuscript in preparation). These data suggest that HIF-VHL oxygen-sensing pathway controls endothelial CXCR4 expression and nerve-derived CXCL12 navigates CXCR4+ endothelial cells to develop co-patterning of neuro-vascular branching. 2) Sympathetic innervation of blood vessels in the developing skin. We are interested in examining how sympathetic axons innervate not only blood vessels but also a wide array of target tissues. Our comprehensive whole-mount imaging of embryonic skin demonstrates that after the establishment of co-branching between sensory nerves and blood vessels, sympathetic axons invade the skin alongside these sensory nerves and extend their branches towards these large-diameter blood vessels. Moreover, VSMC-specific Ngf knockout leads to a significant decrease of collateral branching of sympathetic axons innervating VSMC-covered large-diameter blood vessels (Li et al. Manuscript in preparation). These data suggest that VSMC-derived NGF serves as an inductive signal for collateral branching of sympathetic axons innervating large-diameter blood vessels in the embryonic skin. 3) Development of functional neuro-vascular networks. We have developed a novel in vivo Ca2+ imaging system of embryonic forelimb skin using sensory neuron-specific Ca2+ indicator mice: a knock-in mouse line in which the expression of GCaMP3, a calcium indicator whose green fluorescence intensity is driven by a sensory neuron-specific phosphoinositide-binding protein (Pirt) promoter. The limb skin is dissected from Pirt-GCaMP3 embryos, and sensory neurons are stimulated by capsaicin. We have successfully demonstrated GCaMP3 fluorescence in response to the capsaicin stimuli. We are currently attempting 1) to carry out the time course analysis to study the relationship between sensory activity and the processes of neuro-vascular co-patterning and 2) to examine what happens to sensory activity in the loss-of-function Cxcl12 or Cxcr4 mutants having neuro-vascular mis-patterning. 4) Neuro-vascular networks in pathological situations including obesity-related nerve disorders. We have developed a high-resolution whole-mount imaging method to analyze neuro-vascular branching in the entire ear skin of adult mice. This method enabled us to visualize branching morphogenesis and patterning of peripheral nerves and blood vessels in the animal models of obesity and type 2 diabetes, with comprehensive quantification measurements (Yamazaki et al. 2018 Sci Rep). To examine whether sensory functions are affected before or after such morphological abnormalities in the neuro-vascular branching, we are currently attempting to carry out Pirt-GCaMP imaging, in combination with high-resolution whole-mount imaging, to visualize changes in Ca2+ transient and neuro-vascular branching in the adult ear skin of Pirt-GCaMP3 heterozygous diet induced obesity (DIO) mice. Our ongoing studies demonstrate that sensory hypersensitivity occurs prior to sensory axon degeneration and blood vessel/capillary abnormalities in the DIO skin (Koui, Song, et al. Manuscript in preparation). We are currently investigating what controls sensory hypersensitivity in the DIO skin.